1. Technical Field
This disclosure relates generally to oil and gas well logging and directional drilling. More specifically, techniques are disclosed for enhancing well placement using logging while drilling (LWD) tool data to update or change the reservoir model while drilling, or after drilling. Continuously updating the reservoir model enhances the ability to geo-steer the drill string to the desired location in high angle or horizontal (HA/HZ) wellbores. The disclosed techniques include improved 1D, 2D, 2.5D and 3D modeling methods while drilling using directional electromagnetic, borehole imaging and bit resistivity data. Methods for processing such electromagnetic data are used to model and visualize the layered subterranean earth formations surrounding the tool. The disclosed methods can be used in the well placement planning process to evaluate and select the best measurements to be used in real-time and prepare for unaccounted possible effects. Other measurements and high performance computing modeling methods for processing those measurements are disclosed as well. A high performance computing (HPC) infrastructure and modeling/inversion algorithm library or database is also disclosed. The disclosed methods are not limited to high-angle and horizontal wells and are applicable to vertical and deviated wells and related well placements. The disclosed methods may also apply to related (after-drilling) applications, be they LWD or wireline.
2. Description of the Related Art
Wellbores drilled through earth formations to extract petroleum are frequently drilled along a substantially horizontal trajectory to increase the drainage area, or the length of the wellbore that is disposed within the reservoir. Often, the terms high angle/horizontal or HA/HZ, are used with these types of wellbores. Because petroleum rich reservoirs are frequently located in layered subterranean earth formations, the position or placement of the substantially horizontal wellbore relative to the upper and lower boundaries of the reservoir will have a material effect on the productivity of the wellbore. This disclosure, in addition to HA/HZ wellbores, is more generally directed to vertical and deviated wellbores.
An alternative to wireline logging techniques is the collection of data on downhole conditions during the drilling process. By collecting and processing such information during the drilling process, the driller can modify or correct key steps of the operation to optimize well performance. Schemes for collecting data of downhole conditions and movement of the drilling assembly during the drilling operation are known as measurement-while-drilling (“MWD”). Similar techniques focusing more on measurement of formation parameters than on movement of the drilling assembly are known as logging-while-drilling (“LWD”). However, the terms MWD and LWD are often used interchangeably, and the use of either term in this disclosure will be understood to include both the collection of formation and borehole information, as well as data on movement and placement of the drilling assembly.
Recent introduction of deep directional electro-magnetic (EM) logging tools has revolutionized wellbore placement. Along with real-time borehole imaging technology, the new measurements enable proactive geo-steering, which allow the driller to maintain the well position within the reservoir of interest or “pay zone.” As a result, wellbores are now routinely steered along a path defined by observed reservoir boundaries and fluid contacts rather than by preconceived geometries. Data from the MWD or LWD tools are used for real-time prediction and visualization of the layer structure of the formation surrounding the tool or drill string.
Such real-time visualization allows operators to control the direction of the wellbore drilling operations in order to place or “land” the wellbore in a particular section of a reservoir. Wellbore placement optimization results in increased production by minimizing gas or water breakthrough, reducing sidetracks, and managing drilling risk through better control of the wellbore placement.
Electromagnetic (EM) induction and propagation-style logging tools are well suited for these geo-steering applications because of their relatively large lateral depth of investigation into the surrounding formation. Directional EM LWD tools are available, such as Schlumberger's PERISCOPE™ deep imaging LWD tools, which incorporate multiple tilted and transverse antennas in the drilling collar. The non-axial antennae obtain directional electromagnetic measurements that are used to determine distance and azimuthal orientation of formation boundaries in any type of mud. These measurements are transmitted up-hole in real-time and displayed on a graphical interface (visualized) to provide information on distance to boundaries, formation resistivity and orientation. These EM LWD tools also include short coil spacings for shallow depths of investigation (DOI) or the formation layers near the tool as well as longer coil spacings for deep DOIs or properties of formation layers farther away from the tool. Schlumberger's GEOVISION™ resistivity at the bit tools can be used for geological analysis as well as geo-steering. One component of bit resistivity measurements (also referred to as resistivity-at-the-bit or “RAB”) is azimuthally focused sensors for wellbore positioning.
Current geo-steering solutions provide for two and three dimensional modeling and visualization of both shallow and deep formation properties (see commonly owned U.S. Pat. Nos. 6,594,584 and 7,366,616, incorporated herein by reference). However, the following common scenarios can adversely affect the modeling of a formation: nearby boundaries and faults; cross-bedding; layering; eccentralization of the tool in the borehole; effects of invaded fracture swarms with the presence of nearby boundaries; borehole size variation, shape and mud properties; and others. One or more of these scenarios can cause inconsistencies in model-based interpretations, be they in real-time or post-drilling. Accordingly, improved modeling techniques are needed for enhancing the ability to properly land and drill wellbores in relatively thin reservoirs.